Memory devices are typically provided as internal, semiconductor, integrated circuits and/or external removable devices in computers or other electronic devices. There are many different types of memory including volatile and non-volatile memory. Volatile memory can require power to maintain its data and can include random-access memory (RAM), dynamic random access memory (DRAM), and synchronous dynamic random access memory (SDRAM), among others. Non-volatile memory can provide persistent data by retaining stored data when not powered and can include NAND flash memory, NOR flash memory, read only memory (ROM), and resistance variable memory such as phase change random access memory (PCRAM), resistive random access memory (RRAM), and magnetic random access memory (MRAM), among others.
Memory devices can be combined together to form a solid state drive (SSD), an embedded MultiMediaCard (e.MMC), and/or a universal flash storage (UFS) device. An SSD, e.MMC, and/or UFS device can include non-volatile memory (e.g., NAND flash memory and/or NOR flash memory), and/or can include volatile memory (e.g., DRAM and/or SDRAM), among various other types of non-volatile and volatile memory. Non-volatile memory may be used in a wide range of electronic applications such as personal computers, portable memory sticks, digital cameras, cellular telephones, portable music players such as MP3 players, movie players, among others.
Flash memory devices can include memory cells storing data in a charge storage structure such as a floating gate, for instance. Flash memory devices typically use a one-transistor memory cell that allows for high memory densities, high reliability, and low power consumption. Resistance variable memory devices can include resistive memory cells that can store data based on the resistance state of a storage element (e.g., a resistive memory element having a variable resistance).
Memory cells can be arranged into arrays, and memory cells in an array architecture can be programmed to a target (e.g., desired) state. For instance, electric charge can be placed on or removed from the charge storage structure (e.g., floating gate) of a flash memory cell to program the cell to a particular data state. The stored charge on the charge storage structure of the cell can indicate a threshold voltage (Vt) of the cell. A state of a flash memory cell can be determined by sensing the stored charge on the charge storage structure (e.g., the Vt) of the cell.
As an additional example, resistive memory cells can be programmed to store data corresponding to a target data state by varying the resistance level of the resistive memory element. Resistive memory cells can be programmed to a target data state (e.g., corresponding to a particular resistance state) by applying sources of an electrical field or energy, such as positive or negative electrical pulses (e.g., positive or negative voltage or current pulses) to the cells (e.g., to the resistive memory element of the cells) for a particular duration. A state of a resistive memory cell can be determined by sensing current through the cell responsive to an applied interrogation voltage. The sensed current, which varies based on the resistance level of the cell, can indicate the state of the cell.
A single level memory cell (SLC) can be programmed to a targeted one of two different data states, which can be represented by the binary units 1 or 0. Some flash and resistive memory cells can be programmed to a targeted one of more than two data states (e.g., 1111, 0111, 0011, 1011, 1001, 0001, 0101, 1101, 1100, 0100, 0000, 1000, 1010, 0010, 0110, and 1110). Such cells may be referred to as multi state memory cells, multiunit cells, or multilevel cells (MLCs). MLCs can provide higher density memories without increasing the number of memory cells since each cell can represent more than one digit (e.g., more than one bit).